This application is a 371 of PCT/NL99/00651 filed Oct. 20, 1999.
The invention relates in the first instance to a method for removing a component from a solid particle material by extraction, in which an extraction liquid is brought in flowing contact with the particle material inside a column in which at least one tube extends, and the particle material is fed in at the first end of the column andxe2x80x94forced by hydraulic pressurexe2x80x94moves as a packed porous bed to scraping means fitted at the second end of the column, and the extraction liquid is fed into the column at the above-mentioned second end and flows in countercurrent to the particle material in the direction of the above-mentioned first end of the column, and the particle material is scraped off at the above-mentioned second end by the above-mentioned scraping means.
Such a method is disclosed in FR-A-2.213.080.
In the case of a known method the particle material for extraction and the extraction agent are in a number of successive vessels, the vessels with particle material being conveyed batchwise in a certain direction and the extraction agent being pumped in the opposite direction from one vessel to the next. The particle material gradually loses the above-mentioned component, and the extraction agent takes up said component. The bed of particle material stops in each vessel and the liquid extraction agent flows through it. Although on a macro scale this can be described as a countercurrent process, on a micro scale there is no question of countercurrent here. The process is relatively slow, and the extraction yield leaves something to be desired.
Another known process is described by George C. Blytas in xe2x80x9cChemical Engineering Communicationxe2x80x9d, 1990, Vol. 88, pp. 127-151, under the title xe2x80x9cContinuous countercurrent solid-liquid contacting in rotary disc contactorsxe2x80x9d. A column with discs placed above one another is described in this article. The force of gravity causes solid particles of resin to fall from the top to the bottom of the column and to absorb benzene from an upward-flowing supply stream. Situated between the perforated plates are siring elements which rotate at high speed in order to suspend the particle material. The particle material consists of, for example, resin. This process is also slow and can be carried out only when the particle material settles sufficiently in the extraction agent.
The object of the invention is to provide a method of the type described in the preamble which leads to a relative high speed and a relative high yield and which does not have the disadvantages of the known methods.
According to the invention, the method is characterized in that at least one filter is fitted in the wall of each tube and that extraction liquid with component from the particle material dissolved in said extraction liquid passes by way of the above-mentioned filter or filters into the above-mentioned tube and flows in countercurrent to the particle material to an outlet at the above-mentioned first end, said outlet being connected to the tube, and that the scraped particles are discharged via a washing chamber.
It is important that the solid bed of particle material is moved, forced by hydraulic pressure, in the column, which hydraulic pressure is produced as a result of the filtration resistance of the porous bed of particle material present in the column. The process is preferably a continuous countercurrent process. The main advantage is that a relatively high speed and a high yield are achieved. The material to be extracted is, for example, crushed rapeseed, and the extraction agent hexane. The hexane extracts the oil from the rapeseed.
In order to ensure that a certain extraction by immersion is achieved before the particle material is conveyed into the column, the particle material is mixed beforehand in a tank with extraction agent or a mixture of extraction agent and the above-mentioned component.
The particles which are scraped off at the above-mentioned second end of the column and pass into a washing chamber situated below the scraping means are taken up in a circulating stream of clean extraction agent.
Part of the extraction agent, and a component dissolved therein leaving the tubes at the above-mentioned first end of the column, can be conveyed to the particle material to be fed into the column, while most of said extraction agent is conveyed to a separator for separating extraction agent and component from each other.
In order to limit the consumption of extraction agent, the mixture of extraction liquid and extracted particle material (extracted meal) leaving the column at the above-mentioned second end is separated, and the extraction agent resulting therefrom is pumped back to the above-mentioned second end.
A better yield is generally achieved when the extraction agent is at a raised temperature.
The invention also relates to a device for removing a component from solid particle material by extraction according to claim 1, comprising a column in which at least one tube extends, said column having a first and second end, means for feeding extraction liquid into the column at the second end thereof, and scraping means at the first end of the column for scraping off particle material from a packed porous bed.
Such a device is also disclosed in FR-A-2.213.080.
According to the invention the device is characterized in that in the wall of each tube at least one filter is fitted, that at the first end the outlet is connected to the tube or tubes, and a washing chamber is situated near the scraping means so that scraped off particles are discharged via said washing chamber.